1. Field of the Invention
This invention relates generally to anamorphic lenses, and more particularly to an anamorphic lens having a cylindrical and/or an acylindrical surface, and to an improved photographic camera flash assembly incorporating an anamorphic lens having a cylindrical and/or an acylindrical surface for providing independent illumination control at a target.
2. Description of the Related Art
Illumination assemblies for flash systems of currently popular photographic cameras comprise a trough-type reflector which surrounds a long, slender Xenon flash tube, and a transparent front cover to isolate the flash tube and reflector from physical contact. Front covers typically have optical power to improve the distribution of flash illumination in the object scene being photographed, and thus the front cover can be regarded as a lens.
Sugawara, U.S. Pat. No. 5,160,192, for example, describes an illuminating instrument for decreasing light distribution nonuniformity at an object scene, composed of a multi-ellipsoid reflector, a light source, and a condenser which concentrates light from the flash burst in an object scene. The condenser has an effective convex cylindrical Fresnel lens rear surface in which the Fresnel grooves are perpendicular to the longitudinal axis of the flash tube and a concentric, convex Fresnel front lens surface.
English, U.S. Pat. No. 4,462,063, describes a photo flash assembly which includes an aspheric lens to enhance light output and scene illumination. The aspheric lens has a convexly curving outward surface of either spherical or aspherical shape and a spherical rear, inner surface.
The spherical lens surfaces described by English and Sugawara have the potential to condense object scene illumination in an infinite number of radial directions due to their radial symmetry, while the use of a cylindrical surface, as described by Sugawara, can improve the illumination profile in one direction, for instance, the horizontal or the vertical direction, but the corresponding orthogonal direction is unaffected. Because photographic flash light sources are typically elongate, the use of spherical and cylindrical optical power, separately or in combination, to improve scene illumination, is a compromise attempt to control the illumination distribution in independent, typically orthogonal, directions. To this end, the inventor has recognized a need for an anamorphic lens which is suitable for use in a photo flash assembly, for example, to provide independent illumination control in an object scene in two directions.
Furthermore, as camera flash assemblies get smaller to keep pace with decreasing camera size, flash optical systems require correspondingly shorter focal lengths, and smaller f/#'s, to maintain high picture taking quality. As f/#'s decrease, however, it becomes more difficult to coordinate the destination of light which passes through the edge zone of the lens and the center zone of the lens for the desired object scene illumination distribution, particularly when the lens surface is a cylinder of constant radius. Thus, there is a need to vary the optical power of the lens from the center to the edge zones in order to exercise the necessary control over the scene illumination distribution. To this end, the invention describes an acylindrical, anamorphic lens which has application in a photo flash assembly, for instance, to provide independent illumination control in an object scene in two directions.